Anti-slip device for compressed air brakes, particularly for rail vehicles

ABSTRACT

The invention relates to an anti-slip device for compressed air brakes, particularly for rail vehicles. An anti-slip device for compressed air brakes, particularly for rail vehicles, in which air is admitted to the brake cylinder through a pipe connected to an air reservoir and the brake cylinder is exhausted to atmosphere through an exhaust pipe incorporating a relay valve and a holding valve which closes the exhaust pipe at a prescribed minimum pressure.

United States Patent Keller [151 3,655,246 [4 1 Apr. 11, 1972 [541ANTI-SLIP DEVICE FOR COMPRESSED AIR BRAKES, PARTICULARLY FOR RAILVEHICLES [72] Inventor: Siegfried Keller, Effretikon, Switzerland [73]Assignee: Werkzeugmaschinenfabrik Oerlikon-Buhrle AG, Zurich,Switzerland [22] Filed: Feb. 20, 1970 [21] Appl. N0.: 13,021

[30] Foreign Application Priority Data Feb. 28, 1969 Switzerland..3025/69 [52] US. Cl ..303/21 F, 188/181 A, 303/21 CG ..B60t 8/12..303/2l, 24, 6, 61-63, 303/68-69; 188/181 [51] lnt.Cl. [58]FieldofSearch [5 6] References Cited UNITED STATES PATENTS 2,417,2113/1947 Newell ..303/2l F 2,440,343 4/1948 McCune ..303/21 F PrimaryExaminer-Milton Buchler Assistant Examiner-John J. McLaughlinAttorney-Wenderoth, Lind & Ponack [57] ABSTRACT The invention relates toan anti-slip device for compressed air brakes, particularly for railvehicles. An anti-slip device for compressed air brakes, particularlyfor rail vehicles, in which air is admitted to the brake cylinderthrough a pipe connected to an air reservoir and the brake cylinder isexhausted to atmosphere through an exhaust pipe incorporating a relayvalve and a holding valve which closes the exhaust pipe at a prescribedminimum pressure.

1 Claims, 3 Drawing Figures Patnted A ril 11, 1972 3,655,246

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cl Pz Q R B- E Siegfried Keller, Inventor Attorneys ANTI-SLIP DEVICE FORCOMPRESSED AIR BRAKES, PARTICULARLY FOR RAIL VEHICLES The systematicincrease in railroad speeds has necessitated raising the brake pressureto near the adhesion limit between rail and wheel. Since in suchcircumstances, whenever the rails are in poor condition due to theweather or fouling, the wheels are liable to lock when the brakes areapplied, numerous anti-slip devices for the purpose of avoiding wheellock have been proposed. In principle such anti-slip devices are allbased upon the provision of a sensor on the vehicle axles which respondsto excessive angular deceleration by operating a control valve in theadmission pipe to the brake cylinder, and which thus shuts off thesupply of compressed air to the brake cylinder and exhausts the brakecylinder asquickly as possible. Careful measurements and records made ofall the events that occur in such systems have shown that when the brakecylinders are rapidly exhausted the axle which had been ciritcallydecelerated by the application of the brakes generally already begins toreaccelerate when there is still a residual pressure inside the brakecylinder. In the interests of obtaining the maximum possible brakingeffort, even when the anti-slip device repeatedly responds on slipperyrails, it is therefore desirable not to exhaust the brake cylindersfully before readmitting the air, as has been conventional, but toreduce the pressure only to a predetermined pressure level that has beenascertained by experiment.

For achieving this purpose a prior art system first reduces the brakecylinder pressure when the anti-slip device operates, by quicklyexpanding the air through a large cross section into an associatedcontainer to the desired predetermined pressure and by then allowing thepressure to drop more slowly by exhausting through a throttlingconstriction to atmosphere.

This solution has the drawback that a different expansion capacity isneeded for each size of brake cylinder, and this capacity would have tobe fairly bulky and heavy when the brake cylinders are large.

According to another proposal the brake cylinder is exhausted toatmosphere through a holding valve of large cross section which has beenpreset to maintain the predetermined pressure.

However, this means that in cases where the condition of the rails isparticularly slippery the predetermined pressure may still be highenough to lock the wheels when at the high speed of modern trains thewheels are likely to develop large flats. The object of the presentinvention is to avoid the abovedescribed defects. The proposed anti-slipdevice consists in providing the exhaust pipe between the relay valveand the holding valve with a throttling constriction that continuouslycommunicates with the ambient atmosphere.

This arrangement has the advantage that the air in the brake cylinderwhen the anti-slip device operates will first exhaust through a largecross section to atmosphere until the predetermined pressure is reachedand thereafter, when the holding valve has been closed, more slowlythrough a smaller cross section until the pressure is atmospheric.

With the above and other objects in view which will become apparent fromthe detailed description below, a preferred embodiment of the inventionis shown in the drawings in which:

FIG. 1 is a cross section with parts in elevation of an indirectlyacting compressed air brake associated with an antislip device accordingto the invention, schematically shown, and

FIG. 2 is a graph showing the brake cylinder pressure as a function ofthe distance travelled by the vehicle during wheel slip in equipment ofthe above-described prior art kind, whereas FIG. 3 is a graph showingthe pressure during wheel slip when equipment according to the presentinvention is provided.

Referring to FIG. 1 the main brake pipe of a rail-road carriage notshown in the drawing is connected to a triple distributor valve 11. Thisdistributor valve 11 is connected on the one hand to an air reservoir 12and on the other hand to a relay valve 13. The release pipe of thedistributor valve is at 14.

The relay valve 13 contains a diaphragm l5. Below the diaphragm 12 is achamber 16 which is connected by a pipe 17 to the reservoir 12 forcompressed air. Above the diaphragm 15 is a second chamber 18 which isconnected on the one hand through a constriction 19 and the pipe 17 tothe air reservoir 12 and on the other hand through a pipe 20 to adeceleration sensor 21. The deceleration sensor 21 is mounted on theaxle of a vehicle wheel 22. It is not shown in detail but so contrivedthat when a given deceleration is exceeded it allows air to escape fromthe pipe 20 and hence from the chamber 18.

A stem 23 is attached on the diaphragm 15 of the relay valve 13, thestem carrying a valve disk 24. The valve disk 24 is pressed by a spring25 against a valve seat 26 of the relay valve 13. In the positionillustrated, the valve disk 24 separates a chamber 27 from an exhaustline 28. On the one hand, the distributor valve 11 is connected to thechamber 27 of the relay valve 13 and, on the other hand, a brakecylinder 29 is connected to the said chamber, which cylinder isconnected to an exhaust line 28 in the second position of the valve disk24, which is not illustrated; at the same time, the brake cylinder isdisconnected from the distributor valve.

The exhaust pipe 28 communicates through a holding valve 30 and througha throttling constriction 31 with the'ambient atmosphere. The holdingvalve 30 is designed in the manner of a check valve. The end of theexhaust pipe 28 directly forms a valve seat 32 against which a spring 34presses a valve element 33. The thrust of this spring 34 can be adjustedby means, such as a screw, not specially shown. The inside of the valvecasing is continuously open to atmosphere through an opening 35.

The described anti-slip device functions as follows:

When the brake is released the pressure in the main brake pipe 10 is thenormal system pressure and the air reservoir 12 is full. The pressure inthe two chambers 16 and 18 of the relay valve 14 is likewise the systempressure. The brake cylinder 29 is connected by the relay valve 13 andthe distributor valve 11 to the brake release outlet 14 of thedistributor valve 11 and is therefore exhausted.

For applying the brake the pressure in the main brake pipe is reduced inconventional manner and the distributor valve 11 operates to admit airfrom the air cylinder 12 into the brake cylinder 29, the pressureadmitted into the brake cylinder 29 corresponding to the pressurereduction in the main brake pipe.

If during the application of the brakes the deceleration sensor 21should respond because the rails are slippery, then the chamber 18 ofthe relay valve 13 will exhaust through the pipe 20. The pressureexisting in the chamber 16 of the relay valve 13 causes the valve disc24 to be lifted off the valve seat 26 against the thrust of the spring25 and the air in the brake cylinder 29 can therefore enter the exhaustpipe 28. At the same time the admission of air through the distributorvalve 1 l to the brake cylinder 29 is cut off by the valve disc 24. Assoon as the pressure in the exhaust pipe exceeds a given level the valveelement 33 of the holding valve 30 is raised from its seat 32 againstthe retaining power of its spring 34 and the air can escape from thebrake cylinder 29 until the pressure in the pipe 28 is again less thansaid predetermined level and the holding valve 30 closes again.

The air remaining in the brake cylinder can then gradually continue toescape completely through the throttling constriction 31. The change inpressure in the brake cylinder 29 as a function of the braking distanceS is shown in FIG. 3. The distance A to B corresponds to the pressurefor full application of the brake. Should the deceleration sensor 2]respond because the rails are slippery the pressure will first drop fromB to C for as long as it is still above the level determined by theholding valve 30. When the closing valve 30 shuts the pressure in thebrake cylinder 29 continues to fall more slowly from C to D by the airexhausting through the throttling constriction 31. As soon as thedeceleration sensor 21 ceases to exhaust air from the pipe 20 thepressure will rise again from D to E. If the rails are still slipperythe described process repeats itself.

In contradistinction thereto, as shown in FIG. 2, in the abovepreviously described prior an arrangement the pressure always firstfalls to zero from B to C. The total braking effort which is defined bythe area embraced by the curve is therefore less. In other words,braking takes longer and the distance required for reducing the speed ofthe carriage to a given speed is also longer.

I claim 1. An antiskid device for a compressed air brake of a railroadvehicle, comprising a brake cylinder, a control distribution valve forfilling and emptying said brake cylinder, a deceleration sensorresponding to the deceleration of a wheel during braking on a slipperyrail, a compressed air holding valve, means closing said holding valvewhen the air pressure drops to a predetermined value, a relay valvehaving a first chamber connected to said brake cylinder, a secondchamber in said relay valve connected to said holding valve, a valvedisk in said relay valve actuated by said deceleration sensor, saidvalve disk in a first position separating said first chamber from saidsecond chamber and in a second position separating said brake cylinderfrom said control distribution valve and connecting it to said secondchamber for a rapid lowering of air pressure in said brake cylinder tothe air pressure predeter' mined by said holding valve in the case of abrief response of said deceleration sensor during the braking action ona slightly slippery rail, an exhaust pipe connecting said relay valveand said holding valve, and a throttling constriction in permanentcommunication with the atmosphere positioned in said exhaust pipe, sothat when said holding valve closes to said predetermined value somepressure remains in the brake cylinder prior to the re-application ofthe brakes, said residual pressure being exhausted through saidthrottling constriction in the case of a long response of saiddeceleration sensor during the braking action on a very slippery rail.

1. An antiskid device for a compressed air brake of a railroad vehicle,comprising a brake cylinder, a control distribution valve for fillingand emptying said brake cylinder, a deceleration sensor responding tothe deceleration of a wheel during braking on a slippery rail, acompressed air holding valve, means closing said holding valve when theair pressure drops to a predetermined value, a relay valve having afirst chamber connected to said brake cylinder, a second chamber in saidrelay valve connected to said holding valve, a valve disk in said relayvalve actuated by said deceleration sensor, said valve disk in a firstposition separating said first chamber from said second chamber and in asecond position separating said brake cylinder from said controldistribution valve and connecting it to said second chamber for a rapidlowering of air pressure in said brake cylinder to the air pressurepredetermined by said holding valve in the case of a brief response ofsaid deceleration sensor during the braking action on a slightlyslippery rail, an exhaust pipe connecting said relay valve and saidholding valve, and a throttling constriction in permanent communicationwith the atmosphere positioned in said exhaust pipe, so that when saidholding valve closes to said predetermined value some pressure remainsin the brake cylinder prior to the re-application of the brakes, saidresidual pressure being exhausted through said throttling constrictionin the case of a long response of said deceleration sensor during thebraking action on a very slippery rail.